Orange County NC Website
Browse       Search
26 <br />watershed protection zones, which can vary based on potential sources of pollutants. <br />Watershed protection areas occur from beyond the critical area allowing an operator to shut <br />down should a spill or other water quality issue arise. Protecting streams between reservoirs is <br />equally important as protecting the reservoirs themselves. <br />Excess Nutrients and Eutrophication <br />Many reservoirs in the southeast are susceptible to eutrophication. Eutrophication is caused by <br />an increased concentration of nutrients within a lake or reservoir that in turn increases algal <br />growth and subsequently reduces water quality. In fact, as algae goes through their life cycle <br />and die off, dissolved oxygen in the water can be greatly reduced, causing fish kills and other <br />adverse impacts. While this is a natural process, changes in land use can greatly increase <br />nutrients reaching a reservoir and accelerate eutrophication. Increased impervious surface area <br />leads to decreased stormwater runoff infiltration, which in turn leads to increased nutrient load in <br />stormwater runoff reaching surface waters. This is currently happening to both Jordan and Falls <br />lakes. <br />Excess nutrients are a problem in many watersheds and therefore researchers have looked at <br />sources, impacts and reduction strategies. Research has shown that headwater streams <br />contribute a larger percentage of nitrogen compared to higher order streams (Alexander, et al., <br />2007). However, due to various biological, chemical, and microbial processes occurring in these <br />smaller streams, less nitrogen may be delivered downstream. On the contrary, higher order <br />perennial streams, while contributing less nitrogen, actually transport more due to stream flow <br />and fewer natural processes occurring in larger streams (Alexander, et al., 2000). This <br />underscores the need for protecting both headwater and larger streams, but they may require <br />different methods to protect them. <br />Watershed Protection Measures <br />One protection method includes riparian buffers. Forested buffers along streams can reduce <br />nitrogen loading from stormwater runoff. To be most effective, stormwater runoff needs to <br />infiltrate where soil processes remove more nitrogen (Mayer, et al., 2005). Stream buffers also <br />reduce erosion and sediment reaching streams. They are particularly important in temperature <br />regulation of perennial streams. Shade from trees maintained along streams keeps surface <br />water cooler and cooler water contains more dissolved oxygen that is needed by fish and other <br />aquatic species. Stream buffers are especially useful in protecting smaller headwater streams, <br />helping to maintain the natural biological, chemical and microbial processes that occur in these <br />streams. <br />Riparian buffers are also important for larger streams, but due to the reasons previously <br />discussed, other protections may be warranted. Since excess nutrients (especially nitrogen) are <br />a major concern locally and larger streams have increased transport rates due to stream flow, <br />buffers may not be able to assimilate all of the excess. Encouraging infiltration of stormwater <br />runoff is key. Managing imperviousness by allowing lower development densities can <br />encourage greater infiltration. Preservation of open space and cluster development also <br />encourages infiltration of runoff. This is why the state prescribes watershed protection areas <br />beyond the designated critical area. These protection measures, such as lower density and <br />lower imperviousness, regulate both land and water resources that can adversely affect water <br />quality within water supply reservoirs. <br />Page 2 of 3 <br />